Sulfur-doped composite catalyst, preparation method and application thereof, oxygen evolution electrode and electrolytic bath

Abstract

The invention relates to the field of hydrogen production through alkaline membrane electrolysis of water, and discloses a sulfur-doped composite catalyst and a preparation method and application thereof, electrode slurry, an oxygen evolution electrode and an electrolytic bath, the composite catalyst contains Ni, Fe, S and Mn, the molar ratio of Ni to Fe to S to Mn is (5-20): (1-8): (2-10): 1, and the composite catalyst is a heterostructure of external sulfide and internal alloy. According to the invention, sulfur is doped in the catalyst, and ternary metals of nickel, iron and manganese are compounded, so that the oxygen vacancy density of the material is increased, and the charge transfer capability and the oxygen evolution capability are improved.

Description

Technical Field

[0001] This invention relates to the field of alkaline membrane electrolysis for hydrogen production, specifically to sulfur-doped composite catalysts, their preparation methods and applications, electrode slurries, oxygen evolution electrodes, and electrolyzers. Background Technology

[0002] Hydrogen energy, hailed as the "ultimate energy of the 21st century," is a recognized clean energy source. With finite reserves and increasing consumption of non-renewable fossil fuels such as oil, natural gas, and coal, the development and application of hydrogen energy has become a strategic choice. Currently, water electrolysis for hydrogen production is considered one of the most environmentally friendly and promising methods due to its advantages, including requiring water as a raw material and producing high-purity, pollution-free hydrogen.

[0003] Alkaline electrolysis (AEM) for hydrogen production offers several advantages over traditional alkaline electrolysis technologies, including lower cost and higher efficiency, as it utilizes cost-effective anion exchange membranes, non-precious metals as catalysts, and low-concentration alkaline solutions or water as electrolytes. This makes it a promising next-generation water electrolysis technology. However, AEM is still under development and faces several critical technical challenges. The oxygen evolution reaction (OER) involves a four-electron transfer process with complex and slow kinetics, often resulting in high overpotentials that significantly impact electrolysis efficiency. Currently, commercially available OER catalysts are expensive and limited in reserves, making the development of efficient and stable non-precious metal OER materials crucial for the advancement of AEM technology.

[0004] Although numerous studies on OER electrocatalysts in alkaline media have been reported in the literature, their application in AEMWE is still relatively limited. Oxides and hydroxides have attracted widespread attention due to their low cost and good oxygen evolution reaction activity, but they still fall short of practical application requirements, and their performance and stability need further improvement. Summary of the Invention

[0005] The purpose of this invention is to overcome the problem that the performance of NiFe-based oxygen evolution catalysts in the prior art needs to be further improved, and to provide a sulfur-doped composite catalyst, its preparation method and application, electrode paste, oxygen evolution electrode and electrolytic cell. This composite catalyst has a high oxygen vacancy density and strong charge transfer and oxygen evolution capabilities.

[0006] To achieve the above objectives, the present invention provides a sulfur-doped composite catalyst containing Ni, Fe, S and Mn, wherein the molar ratio of Ni, Fe, S and Mn is 5-20:1-8:2-10:1.

[0007] The second aspect of the present invention provides a method for preparing a sulfur-doped composite catalyst, the method comprising: mixing a nickel source, an iron source, a manganese source and a sulfur source in the presence of a solvent and an alkaline substance and then performing hydrothermal crystallization; performing solid-liquid separation after hydrothermal crystallization; and calcining the solid obtained from the solid-liquid separation in a reducing atmosphere, wherein the amounts of the nickel source, iron source, manganese source and sulfur source are such that the molar ratio of Ni, Fe, S and Mn in the composite catalyst is 5-20:1-8:2-10:1.

[0008] A third aspect of the present invention provides a sulfur-doped composite catalyst prepared by the method described in the second aspect.

[0009] A fourth aspect of the present invention provides an oxygen evolution electrode comprising the sulfur-doped composite catalyst described in the first or third aspect.

[0010] The fifth aspect of the present invention provides an electrolytic cell, wherein the anode of the electrolytic cell is the oxygen evolution electrode described in the fourth aspect.

[0011] The sixth aspect of the present invention provides the application of the sulfur-doped composite catalyst described in the first or third aspect in the electrolysis of water to produce hydrogen.

[0012] Through the above technical solution, the present invention can achieve at least the following beneficial effects: by doping sulfur into the catalyst and combining it with ternary metals such as nickel, iron and manganese, the present invention increases the oxygen vacancy density of the material, improves the charge transfer ability and oxygen evolution ability, and when it is used as an anode to assemble an electrolytic cell, it also has excellent stability. Attached Figure Description

[0013] Figure 1 This is a high-resolution transmission electron microscope (HRTEM) image of the sulfur-doped composite catalyst in Example 1. Figure 2 The energy spectrum of the sulfur-doped composite catalyst in Example 1 is shown. Figure 3 The image shows a transmission electron microscope (TEM) image (left) and a surface scan distribution map of sulfur element (right) of the sulfur-doped composite catalyst in Example 1. Figure 4 The LSV polarization curve of the sulfur-doped composite catalyst in Example 1 is shown. Figure 5 The Tafel slope of the sulfur-doped composite catalyst in Example 1; Figure 6 Electron paramagnetic resonance (EPR) tests of the sulfur-doped composite catalyst in Example 1; Figure 7 SEM image of the sulfur-doped composite catalyst in Example 7; Figure 8 SEM image of the sulfur-doped composite catalyst in Example 7; Figure 9 This is a SEM image of the catalyst in Comparative Example 1. Detailed Implementation

[0014] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0015] In one aspect, the present invention provides a sulfur-doped composite catalyst containing Ni, Fe, S and Mn, wherein the molar ratio of Ni, Fe, S and Mn is 5-20:1-8:2-10:1.

[0016] In this invention, preferably, the molar ratio of Ni, Fe, S and Mn in the composite catalyst is 8-15:2-5:3-5:1.

[0017] This invention increases the oxygen vacancy density of the catalyst by doping it with sulfur and using a ternary metal composite of nickel, iron, and manganese, thereby improving the charge transfer and oxygen evolution capabilities. Furthermore, when used as an anode in an electrolytic cell, it exhibits excellent stability. In particular, doping sulfur in a specific ratio into the composite catalyst significantly reduces the oxygen evolution overpotential and increases the catalyst's activity.

[0018] In this invention, preferably, the composite catalyst is used at a current density of 10 mA / cm². 2 The oxygen evolution overpotential is 150-200mV, more preferably 155-175mV (for example, it can be any two values ​​formed by 155mV, 158mV, 160mV, 162mV, 164mV, 168mV, 170mV, 172mV, 175mV, and the value within the range).

[0019] In this invention, preferably, the Tafel slope of the composite catalyst is 60-80 mV / dec, more preferably 65-75 mV / dec (for example, it can be any two values ​​from 65 mV / dec, 66 mV / dec, 67 mV / dec, 68 mV / dec, 69 mV / dec, 70 mV / dec, 71 mV / dec, 72 mV / dec, 73 mV / dec, 74 mV / dec, 75 mV / dec, and values ​​within that range).

[0020] In this invention, the electron paramagnetic resonance (EPR) test of the sulfur-doped composite catalyst shows that the sulfur-doped composite catalyst can significantly increase the number of oxygen vacancies in the catalyst, thereby increasing the vacancy density and making the catalyst have higher catalytic activity.

[0021] In this invention, preferably, the sulfur-doped composite catalyst has a spherical structure with an average particle size of 10-100 nm, more preferably 20-35 nm (for example, it can be any two values ​​from 20 nm, 21 nm, 22 nm, 23 nm, 24 nm, 25 nm, 26 nm, 27 nm, 28 nm, 29 nm, 30 nm, 31 nm, 32 nm, 33 nm, 34 nm, 35 nm, forming a range and values ​​within that range).

[0022] In this invention, preferably, sulfur is distributed on the surface of the composite catalyst in the form of metal sulfides.

[0023] In this invention, preferably, the metal elements in the composite catalyst exist in the form of metal sulfides and alloys.

[0024] In this invention, preferably, the average thickness of the sulfur-containing surface layer is 1-3 nm (for example, it can be any two values ​​formed by 1 nm, 1.2 nm, 1.4 nm, 1.6 nm, 1.8 nm, 2 nm, 2.2 nm, 2.4 nm, 2.6 nm, 2.8 nm, and 3 nm, or a value within that range).

[0025] The second aspect of the present invention provides a method for preparing a sulfur-doped composite catalyst, the method comprising: mixing a nickel source, an iron source, a manganese source and a sulfur source in the presence of a solvent and an alkaline substance and then performing hydrothermal crystallization; performing solid-liquid separation after hydrothermal crystallization; and calcining the solid obtained from the solid-liquid separation in a reducing atmosphere, wherein the amounts of the nickel source, iron source, manganese source and sulfur source are such that the molar ratio of Ni, Fe, S and Mn in the composite catalyst is 5-20:1-8:2-10:1.

[0026] In this invention, the composite catalyst prepared by the above method increases the oxygen vacancy density of the material, improves the charge transfer ability and oxygen evolution ability, and also has excellent stability when it is used as an anode to assemble an electrolytic cell.

[0027] In this invention, preferably, the amount of nickel source, iron source, manganese source and sulfur source in the composite catalyst is such that the molar ratio of Ni, Fe, S and Mn in the composite catalyst is 8-15:2-5:3-5:1.

[0028] It is understood that the statement that "the amount of nickel source, iron source, manganese source and sulfur source makes the molar ratio of Ni, Fe, S and Mn in the composite catalyst 5-20:1-8:2-10:1" does not limit the amount of nickel source, iron source, manganese source and sulfur source to be the same as the molar ratio of Ni, Fe, S and Mn in the final composite catalyst, but is only used to reflect the molar ratio of Ni, Fe, S and Mn in the composite catalyst.

[0029] In this invention, preferably, the molar ratio of nickel source (calculated as nickel), iron source (calculated as iron), sulfur source (calculated as sulfur), and manganese source (calculated as manganese) in the composite catalyst is 1-20:0.1-6:0.5-25:1, more preferably 2-16:0.5-5:3.5-13:1.

[0030] In this invention, the sulfur source can be an external sulfur source, but when the nickel, iron, and manganese sources contain sulfur, an external sulfur source may not be required. Preferably, the sulfur source can be an external sulfur source and / or at least one of a (sulfur-containing) nickel, iron, and manganese source; more preferably, the sulfur source is at least one of a (sulfur-containing) nickel, iron, and manganese source. In particular, when the sulfur source is at least one of a (sulfur-containing) nickel, iron, and manganese source, the nickel, iron, and manganese sources can be nickel sulfate, ferric sulfate, and manganese sulfate, etc.

[0031] In this invention, preferably, the nickel source can be a substance commonly used in the art to provide nickel for sulfur-doped composite catalysts, for example, it can be at least one of nickel sulfate, nickel nitrate and nickel chloride.

[0032] In this invention, preferably, the iron source can be a substance commonly used in the art to provide iron to sulfur-doped composite catalysts, for example, it can be at least one of ferric sulfate, ferric nitrate and ferric chloride.

[0033] In this invention, preferably, the manganese source can be a substance commonly used in the art to provide manganese element for sulfur-doped composite catalysts, for example, manganese sulfate and / or manganese chloride.

[0034] In this invention, preferably, the external sulfur source can be a substance commonly used in the art to provide sulfur element to sulfur-doped composite catalysts, for example, sodium sulfate and / or sodium bisulfate.

[0035] In this invention, preferably, the alkaline substance, calculated as hydroxide ions, is added at 1-20 times the total molar amount of nickel, iron, and manganese, more preferably at 2.5-10 times (for example, it can be any two multiples from 2.5 times, 3 times, 3.5 times, 4 times, 4.5 times, 5 times, 5.5 times, 6 times, 6.5 times, 7 times, 7.5 times, 8 times, 8.5 times, 9 times, 9.5 times, 10 times, forming a range and multiples within that range).

[0036] In this invention, preferably, the alkaline substance can be selected from alkali metal hydroxides and / or ammonia monohydrate, and more preferably, it can be sodium hydroxide and / or potassium hydroxide.

[0037] In this invention, there is no particular limitation on the solvent. It can be any solvent commonly used in the art that can dissolve nickel, iron, manganese and sulfur sources, such as water. There is no particular limitation on the amount of solvent used, as long as it can fully mix the iron and cobalt sources.

[0038] In this invention, preferably, the conditions for hydrothermal crystallization are as follows: the hydrothermal crystallization temperature can be 100-200℃, more preferably 120-150℃ (for example, it can be any two values ​​from 120℃, 122℃, 124℃, 126℃, 128℃, 130℃, 132℃, 134℃, 136℃, 138℃, 140℃, 142℃, 144℃, 146℃, 148℃, 150℃, or any value within that range); the hydrothermal crystallization time can be 8-36h, more preferably 12-24h (for example, it can be any two values ​​from 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, 20h, 21h, 22h, 23h, 24h, or any value within that range).

[0039] In a preferred embodiment of the present invention, the solid-liquid separation can be performed using methods commonly used in the art, such as vacuum filtration; wherein, the vacuum filtration process can be performed with the addition of deionized water.

[0040] In this invention, preferably, the calcination process may also involve the presence of a protective gas, wherein the protective gas may be nitrogen and / or an inert gas.

[0041] In this invention, preferably, there is no special limitation on the reducing gas; for example, it can be hydrogen.

[0042] In this invention, preferably, the mass ratio of hydrogen to protective gas can be 1:5-9 (for example, it can be any two ratios from 1:5, 1:6, 1:7, 1:8, 1:9, or any ratio within that range).

[0043] In this invention, preferably, the roasting conditions may include: 300-600℃, more preferably 350-550℃ (for example, any two values ​​from 350℃, 360℃, 380℃, 400℃, 420℃, 440℃, 460℃, 480℃, 500℃, 520℃, 540℃, 550℃, or any value within that range); the roasting time is 1-5h, more preferably 2-4h (for example, any two values ​​from 2h, 2.5h, 3h, 3.5h, 4h, or any value within that range).

[0044] In this invention, preferably, the calcination temperature can be achieved by heating at a rate of 2-10℃ / min (for example, it can be any two values ​​formed by 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, and 10℃ / min, or values ​​within that range), wherein the calcination time is the time when the calcination temperature is reached and the timing begins.

[0045] A third aspect of the present invention provides a sulfur-doped composite catalyst prepared by the method described in the second aspect.

[0046] A fourth aspect of the present invention provides an oxygen evolution electrode comprising the sulfur-doped composite catalyst described in the first or third aspect.

[0047] In this invention, the oxygen evolution electrode can be prepared using methods commonly used in the art, and the substances added during the preparation process are also commonly used in the art for preparing oxygen evolution electrodes.

[0048] The fifth aspect of the present invention provides an electrolytic cell, wherein the anode of the electrolytic cell is the oxygen evolution electrode described in the fourth aspect.

[0049] The sixth aspect of the present invention provides the application of the sulfur-doped composite catalyst described in the first or third aspect in the electrolysis of water to produce hydrogen.

[0050] The present invention will be described in detail below through examples. In the following examples, the perfluorosulfonic acid polymer (Nafion) is a commercially available product of Innocare, brand name Nafion117; the anion exchange membrane (AEM, PiperION A5-HCO3) is a commercially available product of Shengerno, brand name Versogen.

[0051] The oxygen vacancy density was measured by electron paramagnetic resonance (EPR); the molar ratio of each element was measured by scanning electron microscopy (S-4800) EDS energy dispersive spectroscopy; the average shell thickness was measured by high-resolution transmission electron microscopy; and the average core particle size was measured by high-resolution transmission electron microscopy.

[0052] Example 1 NiSO4·6H2O (8 mmol), FeSO4·6H2O (2 mmol), MnSO4 (1 mmol), and deionized water (30 mL) were mixed and stirred for 10 minutes. Then, 10 mL of KOH solution (1 mol / L) was added dropwise, and stirring continued for another 10 minutes. Subsequently, the mixture was placed in a Teflon (polytetrafluoroethylene) pressure reactor and hydrothermally crystallized at 120 °C for 24 hours. Finally, the solution was filtered with deionized water, and the recovered solid was vacuum dried overnight to obtain the NiFeMn precursor. The synthesized NiFeMn precursor was heated to 370 °C in 10 wt% Ar / H2 (H2 mass content was 10%) at a heating rate of 5 °C / min, and then calcined for 2.5 hours. It was then dried for later use. The high-resolution transmission electron microscopy of the prepared sulfur-doped composite catalyst is shown in the figure below. Figure 1 As shown, the energy spectrum results are as follows: Figure 2 As shown, Figure 3 The images show a transmission electron microscope (TEM) image (left) and a surface scan distribution map of sulfur (S) for the sulfur-doped composite catalyst of Example 1 (right). From the above... Figure 1-3 It is known that the catalyst particle size is about 20 nm. The catalyst consists of two parts: a surface layer and a core. Sulfur is mainly distributed in the form of sulfides on the surface of the particles. The surface layer thickness is about 2 nm. The molar ratio of Ni:Fe:Mn:S in the composite catalyst is 12:3:1:5.

[0053] Weigh 10 mg of the catalyst and 4 mg of XC-72 conductive carbon black, add them to 1.5 mL of isopropanol and 0.5 mL of water, and sonicate for 60 min. Then add 80 μL of Nafion (perfluorosulfonic acid polymer) and sonicate for 10 min. Take 5 μL of the dispersion each time, 3 times, and add it dropwise to a rotating disk electrode for testing the oxygen evolution performance of water electrolysis.

[0054] A three-electrode system was constructed using a rotating disk electrode loaded with catalyst as the working electrode, a graphite rod as the counter electrode, a standard hydrogen electrode as the reference electrode, and 1M KOH solution as the electrolyte. The catalyst was activated and stabilized using cyclic voltammetry, and its OER (oxygen evolution reaction) performance was evaluated using linear sweep voltammetry.

[0055] Electrochemical testing was conducted using a Shanghai Chenhua 760E electrochemical workstation. Before testing, N2 was bubbled through the electrolyte for approximately 30 minutes to saturate it. Subsequently, the three-electrode testing system was assembled, with the voltage range set at 0-1.2V (vs. RHE). CV scans were performed for 20 cycles at scan rates of 100mV / s and 50mV / s to ensure complete sample activation and exposure of active sites. LSV testing was then conducted at 1.2-1.8V. Figure 4 (LSV polarization curve for Example 1). At a current density of 10 mA / cm² 2 At that time, the oxygen evolution overpotential of the product was measured to be 172mV. Figure 5 The Tafel slope of the sulfur-doped composite catalyst in Example 1 is 73.3 mV / dec. Figure 6 Electron paramagnetic resonance (EPR) tests were performed on the sulfur-doped composite catalyst of Example 1. Figure 6 This indicates that S doping can significantly increase the vacancy density.

[0056] Example 2 A sulfur-doped composite catalyst was prepared according to the method of Example 1, except that 1 mmol MnSO4 was replaced with 0.5 mmol. The catalyst particle size was approximately 25 nm, and the surface layer thickness was approximately 1.5 nm. The molar ratio of Ni:Fe:Mn:S in the composite catalyst was 12:3:0.6:5. At a current density of 10 mA / cm², the catalyst was tested. 2 At that time, the catalyst oxygen evolution overpotential was 185mV, and the Tafel slope was 75mV / dec.

[0057] Example 3 A sulfur-doped composite catalyst was prepared according to the method of Example 1, except that 1 mmol of MnSO4 was replaced with 3 mmol. The catalyst particle size was approximately 30 nm, and the surface layer thickness was approximately 2 nm. The molar ratio of Ni:Fe:Mn:S in the composite catalyst was 12:3:1.5:5. At a current density of 10 mA / cm²... 2 At that time, the catalyst oxygen evolution overpotential was 170mV and the Tafel slope was 70mV / dec.

[0058] Example 4 A sulfur-doped composite catalyst was prepared according to the method of Example 1, except that the amount of FeSO4·6H2O used was 4 mmol (the molar ratio of nickel source (calculated as nickel) to iron source (calculated as iron) was 2). The catalyst particle size was approximately 35 nm, and the surface layer thickness was approximately 2 nm. The molar ratio of Ni:Fe:Mn:S in the composite catalyst was 12:5:1:5. At a current density of 10 mA / cm²... 2 At that time, the catalyst oxygen evolution overpotential was 159 mV, and the Tafel slope was 65 mV / dec.

[0059] Example 5 A sulfur-doped composite catalyst was prepared according to the method in Example 1, except that the calcination temperature was 450°C. The catalyst particle size was approximately 20 nm, and the surface layer thickness was approximately 2 nm. The molar ratio of Ni:Fe:Mn:S in the composite catalyst was 12:3:1:4. The catalyst was tested at a current density of 10 mA / cm². 2 At that time, the catalyst oxygen evolution overpotential was 170mV and the Tafel slope was 71mV / dec.

[0060] Example 6 A sulfur-doped composite catalyst was prepared according to the method in Example 1, except that the calcination temperature was 550°C. The catalyst particle size was approximately 25 nm, and the surface layer thickness was approximately 1.5 nm. The molar ratio of Ni:Fe:Mn:S in the composite catalyst was 12:3:1:3. The catalyst was tested at a current density of 10 mA / cm². 2 At that time, the catalyst oxygen evolution overpotential was 180mV, and the Tafel slope was 70mV / dec.

[0061] Example 7 The sulfur-doped composite catalyst was prepared according to the method in Example 1, except that the amount of KOH solution (1 mol / L) used was 20 mL. The product morphology is as follows. Figure 7 and Figure 8 As shown, the catalyst particle size is approximately 80 nm, and the surface layer thickness is approximately 3 nm. The molar ratio of Ni:Fe:Mn:S in the composite catalyst is 12:2:1:3. At a current density of 10 mA / cm²... 2 At that time, the catalyst oxygen evolution overpotential was 195mV, and the Tafel slope was 83mV / dec. Figure 7 and Figure 8 SEM image of the sulfur-doped composite catalyst in this embodiment.

[0062] Example 8 A sulfur-doped composite catalyst was prepared according to the method in Example 1, except that the hydrothermal crystallization temperature was 150°C. The catalyst particle size was approximately 30 nm, and the surface layer thickness was approximately 2.5 nm. The molar ratio of Ni:Fe:Mn:S in the composite catalyst was 15:3:1:5. The catalyst was tested at a current density of 10 mA / cm². 2 At that time, the catalyst oxygen evolution overpotential was 170mV and the Tafel slope was 75mV / dec.

[0063] Comparative Example 1 A sulfur-doped composite catalyst was prepared according to the method of Example 1, except that MnSO4 was not added, and the amount of NiSO4·6H2O added was 8.5 mmol, and the amount of FeSO4·6H2O added was 2.5 mmol. At a current density of 10 mA / cm²... 2 At that time, the catalyst oxygen evolution overpotential was 225 mV, and the Tafel slope was 70 mV / dec. Figure 9 This is a SEM image of the catalyst used in this comparative example.

[0064] Comparative Example 2 The catalyst was prepared according to the method of Example 1, except that the equimolar amounts of NiSO4·6H2O, FeSO4·6H2O, and MnSO4 were replaced with Ni(NO3)2·6H2O, Fe(NO3)3·9H2O, and Mn(NO3)2 (i.e., without sulfur doping). The molar ratio of Ni:Fe:Mn in the composite catalyst was 20:5:1. At a current density of 10 mA / cm²... 2 At that time, the catalyst oxygen evolution overpotential was 255mV, and the Tafel slope was 83mV / dec.

[0065] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A sulfur-doped composite catalyst, characterized in that, The composite catalyst contains Ni, Fe, S and Mn, and the molar ratio of Ni, Fe, S and Mn is 5-20:1-8:2-10:

1.

2. The composite catalyst according to claim 1, wherein, In the composite catalyst, the molar ratio of Ni, Fe, S and Mn is 8-15:2-5:3-5:1; And / or, the composite catalyst is used at a current density of 10 mA / cm². 2 The oxygen evolution overpotential is 150-200mV. And / or, the Tafel slope of the composite catalyst is 60-80 mV / dec, preferably 65-75 mV / dec.

3. The composite catalyst according to claim 1 or 2, wherein, The composite catalyst has a spherical structure and an average particle size of 10-100 nm, preferably 20-35 nm. Preferably, sulfur is distributed on the surface of the composite catalyst in the form of metal sulfides; And / or, the metal elements in the composite catalyst exist in the form of metal sulfides and alloys.

4. A method for preparing a sulfur-doped composite catalyst, characterized in that, The method includes: mixing a nickel source, an iron source, a manganese source, and a sulfur source in the presence of a solvent and an alkaline substance, and then performing hydrothermal crystallization; after hydrothermal crystallization, performing solid-liquid separation; and calcining the solid obtained from the solid-liquid separation in a reducing atmosphere. The amounts of nickel source, iron source, manganese source, and sulfur source are such that the molar ratio of Ni, Fe, S, and Mn in the composite catalyst is 5-20:1-8:2-10:

1.

5. The preparation method according to claim 4, wherein, In the composite catalyst, the amounts of nickel source, iron source, manganese source and sulfur source are such that the molar ratio of Ni, Fe, S and Mn in the composite catalyst is 8-15:2-5:3-5:

1. And / or, in the composite catalyst, the molar ratio of nickel source (calculated as nickel), iron source (calculated as iron), sulfur source (calculated as sulfur), and manganese source (calculated as manganese) is 1-20:0.1-6:0.5-25:1, preferably 2-16:0.5-5:3.5-13:

1.

6. The preparation method according to claim 4 or 5, wherein, The nickel source is selected from at least one of nickel sulfate, nickel nitrate, and nickel chloride; And / or, the iron source is selected from at least one of ferric sulfate, ferric nitrate and ferric chloride; And / or, the manganese source is selected from manganese sulfate and / or manganese chloride; And / or, the sulfur source is derived from an external sulfur source and / or at least one of a nickel source, an iron source, and a manganese source; preferably, the sulfur source is derived from at least one of a nickel source, an iron source, and a manganese source. Preferably, the external sulfur source is selected from sodium sulfate and / or sodium bisulfate.

7. The preparation method according to claim 4, wherein, The amount of alkaline substance, calculated as hydroxide ions, is 1-20 times, preferably 2.5-10 times, the total molar amount of nickel, iron, and manganese. And / or, the alkaline substance is selected from alkali metal hydroxides and / or ammonia monohydrate, preferably sodium hydroxide and / or potassium hydroxide.

8. The preparation method according to claim 4 or 5, wherein, The conditions for hydrothermal crystallization include: a hydrothermal crystallization temperature of 100-180℃, preferably 120-150℃; and a hydrothermal crystallization time of 8-36h, preferably 12-24h. And / or, the roasting process also involves the presence of a protective gas; And / or, the calcination conditions include: a calcination temperature of 300-600℃, preferably 350-550℃; and a calcination time of 1-5h, preferably 2-4h. Preferably, the roasting temperature is achieved by heating at a rate of 2-10℃ / min; the roasting time is the time taken after the roasting temperature is reached.

9. The sulfur-doped composite catalyst prepared by the method according to any one of claims 4-8.

10. An oxygen evolution electrode, characterized in that, The oxygen evolution electrode comprises a sulfur-doped composite catalyst as described in any one of claims 1-3 or 9.

11. An electrolytic cell, characterized in that, The anode of the electrolytic cell is the oxygen evolution electrode as described in claim 10.

12. The application of the sulfur-doped composite catalyst according to any one of claims 1-3 or 9 in the electrolysis of water to produce hydrogen.

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